Studies will be performed on patients with heart failure of a variety of causes and on dogs with induced cardiac lesions. The effect of alterations in impedance to left ventricular ejection will be evaluated by the use of drugs which constrict and dilate the peripheral vascular beds. Effect of these agents will be compared to the effect of agents which increase contractility of the left ventricle. A variety of vasodilator drugs will be studied in order to characterize their vascular sites of action and to evaluate their efficacy in restoring more normal hemodynamics in the setting of heart failure. Bibliographic references: Cohn JN, Guiha NH, Broder MI, Limas CJ: Right ventricular infarction: Clinical and hemodynamics features. Am J Cardiol 33: 209-214, 1974. Franciosa JA, Guiha NH, Limas CJ, Paz S, Cohn JN: Arterial pressure as a determinant of left ventricular filling pressure after acute myocardial infarction. Am J Cardiol 34: 506-512, 1974.